This invention is related to acoustical or ceiling panels. Acoustical tiles, also known as acoustical panels, ceiling tiles or ceiling panels, are well known in the building trades for providing a ceiling that is quickly installed, inexpensive and lightweight. The tiles are prepared from a slurry of fillers and binders, most frequently by either a casting process or a felting process.
In the water felting of such a slurry, a dispersion of a filler, a binder and other ingredients flow onto a moving, porous support, such as that of a Fourdrinier or Oliver mat forming machine for dewatering. The dispersion dewaters first by gravity and then vacuum suction means. The wet basemat is dried in heated convection drying ovens and the dried material is cut to the desired dimensions and optionally top coated, such as with paint, to produce acoustical tiles and panels.
Acoustical tile is also made by a wet pulp molded or cast process such as that described in U.S. Pat. No. 1,769,519. A molding composition that includes fibers, fillers, colorants and a binder is prepared for molding or casting the body of the tile. This mixture is placed upon suitable trays which have been covered with paper or a metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller. A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays filled with the pulp are then placed in an oven to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into tiles of a desired size.
Mineral wool is often used as the fiber in ceiling tiles. Optionally, the mineral wool is combined with cellulosic fiber, such as recycled paper fibers. Strength of the ceiling tile panel comes from interlacing of the fibers together with the action of the binder. Although these mechanisms result in a ceiling tile that bears its own weight, the tile is subject to sag over time (years) or when exposed to high temperatures and/or high humidity.
Sag is also more likely to occur because ceiling tiles are normally installed in a horizontal position. This accentuates the effects of gravity. While the edges of the tile are supported, the center of the tile is held in place only by the integrity of the mineral wool matrix from which the tile is made. Over time, gravity tends to pull the interlaced mineral wool fibers apart, weakening the matrix and reducing the dimensional stability. When ceiling tiles bear the weight of insulation above them, or when they are subject to fluctuations in temperature and humidity, such as in a bathroom, an unsightly sag in the tiles can develop.